It is common practice to cast molten metals, particularly ferrous metals such as steel, to form large ingots, and to line the upper portion or head of the ingot mold with slabs or sideboards of a heat-insulating or exothermic material. These slabs or sideboards are often both insulating and exothermic, and serve to delay the loss of heat from the molten metal, thus maintaining its molten state long enough to compensate for shrinkage in the body of the ingot as it solidifies. An assembly of such sideboards in an ingot mold is known as a "hot top." A hot top prevents undesirable voids and shrinkage in the ingot.
Preferred sideboards are heat-insulating sideboards conveniently formed of a low conductivity inorganic fiber or fibrous material, generally asbestos, alumina, glass wool or the like, which may be coated with a well-known exothermic material. As the molten metal contacts the exothermic material sideboard, a large quantity of heat is released. The insulating ability of the sideboard serves to retard dissipation of the heat and the hot top zone.
Conventionally, molds for ingots are more or less rectangular in horizontal section near the top, and are tapered from a large wide base to a relatively small top. Each of the four sides of the generally rectangular downwardly outwardly flaring hot top walls, is provided with a laminar slab or sideboard which is to be securely biased or otherwise held against each side. Conventionally, four sideboards are used which essentially completely cover the inner surfaces of the walls near the top of an ingot mold. The sideboards are inserted manually into the top of an ingot mold and must be secured snugly against the inner walls of the mold before the molten metal is poured into it. The importance of maintaining the sideboards flush against the inner surface of the ingot mold cannot be overstressed since molten metal flowing between the sideboards and the walls of the ingot mold will often ruin an ingot. Again, if the sideboard is not tightly biased against a wall of the ingot mold, it may float to the top and the function of the sideboard is frustrated.
To combat this problem, much effort has been devoted both to the design of the inner liner, including individual sideboards to form an inner liner, and to the means utilized for tightly securing the inner liner against the upper portion of the inner walls of the ingot wall. Over the years, a vast array of devices has been used, or suggested for use, with generally rectangular sideboards, for the sole purpose of providing an effective hot top for an ingot mold. Most of the devices have been discarded sooner or later, either because they are less effective than they should be, or they cost too much, or they are relatively inconvenient and unsafe to install.
It must be kept in mind that each of the aforementioned factors are of the utmost importance. It is unnecessary to reiterate that any means which is not reasonably safe and reliably effective will not be looked upon favorably by a foundry using it. Again, since hot tops are generally limited to usage only by large volume users, such as steel makers, it is of utmost importance the cost be such that the foundry of the steel maker can afford the expenditure. Of course, the retaining means used to secure the sideboards in an ingot mold are not reusable because it melts when molten metal submerges the retaining means.
As has been stated hereinabove, the retaining means for an inner liner is usually installed manually. Typically, a single person sets the liner into the top of the ingot mold, usually while the mold is still uncomfortably hot, and thereafter inserts some type of metal retaining means which he must then set into position by an additional manual operation. Popular means for securing a hot top in an ingot mold are exemplified by the clips disclosed in U.S. Pat. Nos. 3,734,454 and 3,762,033. In each of these devices, it will be noted that over-pieces of wire-ties are provided which must be twisted with a turn-key to secure the hot top. The over-pieces and wire-ties are welded to members which bias the sideboards against the inner walls of the ingot mold.
In still another device disclosed in U.S. Pat. No. 3,362,677, there is described a unitary frame provided with a spring clip at each corner which biases only two sideboards in end-adjacent relationship with each other. Each spring clip has a resilient loop at its vertex, and the arms are provided with small eyes at their ends to enable the spring clips to be deformed inwardly by tie-downs prior to insertion of the frame into a hot top assembly. The ends of the arms of each of the spring clips are freed by cutting the tie-downs so as to provide a biasing force against the sideboards of the inner liner. However, the cost of the frame, the difficulty of fabricating it, the difficulty of installing it, and the problem of effectively biasing the sideboards with the minimal tangential contact provided by the eyes on the ends of the arms of the spring clips, all militate against the popularity of this device.
The hot top assembly of my invention is unfettered by any of the problems of the prior art devices none of which includes two diagonally oppositely disposed L-shaped retainer clips, each of which simultaneously biases all four sideboards due to a resilient loop formed in or near the U-shaped spring end of each arm. Moreover, two sideboards in end-adjacent relationship are biased against the inner walls coextensive therewith by arms of an L-shaped member or retainer clip. The term "retainer clip" rather than "retainer" is used to identify each L-shaped member because a single L-shaped member does not effectively retain all four sideboards. Each retainer clip acts independently of the other, and requires no connecting means therebetween to provide an effective retainer for a hot top. Each arm of a retainer clip overlies a sideboard and extends over a major portion of the length of the sideboard. Furthermore, my retainer clips are particularly desirable because they are easily and relatively inexpensively fabricated, only two being required diagonally oppositely disposed, one from the other. Moreover the retainer clips are easy to handle prior to installation and easy to store.